In the ever-expanding field of bio-engineering and especially in the medico-engineering field, the provision of biocomcompatible, high-strength, conveniently fabricated and formulated products for implants and/or bone replacements is a constantly sought and demanding desideratum. Hydroxyapatite (Ca.sub.5 (PO.sub.4).sub.3 OH) which is the normal and inorganic structural basis of bone has been widely studied and used in the medical and dental fields, and this material is, then, obviously approved by the United States Food and Drug Administration for use in human beings.
All of the apatitic materials, as well as related calcium phosphates presently in use are crystalline materials requiring very high temperatures (e.g. 1400.degree.-1600.degree. C.) with concomitant high degrees of shrinkage (25-50%) in their fabrication into implants and the like.
The use of the highly refractory apatitic compounds and other bio-acceptable calcium phosphates has not been the panacea for the purposes described above since they do not solve the obvious difficulties inherent in the handling of such infusible substances.
Many of the phosphatic compounds also undergo decomposition at the high temperatures found necessary in the fabrication of shaped structures. As described in U.S. Pat. No. 4,135,935 one solution has been to provide a highly siliceous glass matrix for the refractory material (e.g. fluorapatite) and form a shaped body by compressing and molding a comminuted mixture of the finely ground glass and the fluorapatite under very high pressure and then sintering the mass at about 670.degree. C. (1238.degree. F.). The glass may contain a radio-active compound, e.g. thorium oxide (ThO.sub.2) or a ray-absorbing compound such as lead oxide (PbO).
In a related area it is known to provide radiation shielding glass, and specifically, even a phosphate glass. Thus, in U.S. Pat. No. 3,149,234 there is described a low melting, (&lt;350.degree. C.) soft phosphate glass with high amounts of lead, mercury, and/or tantalum. This patent, while mentioning the use of bismuth trioxide and even exemplifying same in but one of twenty-five examples, (and in this example only very small amounts are shown), there is patently no contemplation or suggestion of bio-engineering use; no teaching of a calcium phosphate material, and no provision of a strong, high melting, but workable, glass. U.S. Pat. No. 2,518,194 also discloses an X-ray shielding phosphate glass with high lead and tungsten content. The use of calcium oxide (CaO) is mentioned just once, and, briefly (Col. 3 line 33). but nowhere is it shown as a component in any glass batch.
Some other prior art of interest relates to phosphate ceramic bodies, generally useful as electrical insulating materials In this regard, attention is directed to U.S. Pat. No. 2,486,812 describing a glassy metaphosphate binder for a ceramic body. Generally, the glass matter is comprised of from 85% to 95% by weight of an iron or aluminum phosphate fused with a minor (3 to 15%) amount of fluorspar.
In a similar vein to the foregoing, we also find of interest ceramic glazes and linings. Here we find, illustratively, U.S. Pat. No. 1,654,404 (a phosphatitic material) and U.S. Pat. Nos. 2,204,582, 3,035,937, and 4,481,036, none of which, however are phosphate-containing.